Method of making alloys of iron and steel



Patent ed Dec. 26, 1939 METHOD OF No Drawing.

Claims.

This invention relates to an improved method for alloying metals,particularly iron and steel, with other metals reducible from theiroxides, and more especiallyfor the production of steels v having a highpercentage of the alloying metal with a negligible or low percentage ofcarbon, and the present case is a continuation in part of my applicationfor Letters Patent, Serial No. 147,736, filed under date of June 11,1937, for a Method of making alloys of iron and steel, and whichapplication was allowed under date of October 8, 1938.

Primarily the process 'of the present invention is for alloying a bathof ferruginous molten metal whereby an oxide of the alloying metal incombination with a suitable reducing agent, such as a metal silicide,both in a comparatively fine state of division, are bound together witha suitable hydroxide of an alkaline earth such as slaked lime, or with achloride solution of an alkaline earth, such as chloride of magnesium,and just suflicient water is added to form a plastic mass, the amount ofsuch binding material used being suflicient to bind these ingredientstogether, and to partly flux the silica formed by the chemical reactionsas therein expressed; the quantity of the hydroxide or chloride of analkaline earth needed to effect this, and to maintain the molded piecesor blocks of sufficient density for the purpose when introduced into thefurnace chamber that they will penetrate the slag and come into directcontact with the surface of the bath of ferru-ginous molten metal,generally varies from 10 to 12 parts to 100 parts of the mix (ore andthe metal silicide); the plastic mass is pugged up in any suitable milland may be molded into comparatively heavy pieces or blocks weighingabout 40 to lbs. or more, and may be of any suitable shape and size andweight 49 for the furnace men to handle. These molded pieces or blocks,after being air dried at room temperature, or the drying may be hastenedby a current of air, may preferably be treated with a milk of lime wash,and after being sufiiciently dried are transferred to a suitable oven orkiln where the excess or loosely held water is exing material and thealkaline "earth: together,"

and the air drying of the pieces, and also "of any carbonic acid gas(CO2) that the lime may have Casimir James Head, Montreal, Quebec,Canada,

assignor to Metallurgical Development Company Limited, Montreal, Quebec,Canada, a corporation of Quebec, Canada Application March 25, 1939,Serial No. 264,212

AELLOYS OF IRON AND absorbed'before being charged into the meltingfurnace chamber for alloying purposes.

While in the practical operation of my invention a temperature in excessof 1650 F. has proven satisfactory for freeing the pieces or blocks ofalloying material from free and combined water therein and to degasifysame, nevertheless it has been found that the temperature range foraccomplishing this desirable result, as well as to entirely free thepieces or blocks from gases, is largely dependent upon thecharacteristics and nature of the alloying material and of the alkalineearth used, which are component parts of the molded pieces or blocks,and therefore the temperature may vary from 700 C. to 1000 C. The objectof this final heating within said range of temperatures being toliberate any remaining free water as well as the combined and colloidalwater held by the pieces or blocks, and anycarbonic acid gas that theymay have absorbed, so that when the heated pieces or blocks are chargedinto the furnace chamber, the bath of ferruginous molten metal will notabsorb gases therefrom, and' by virtue of their density, weight, andheat will displace the slag and come into direct contact with thesurface of the molden bath of ferruginous metal, and as the reducedmetal or metals are released from the pieces or blocks they will carrythe heat evolved by the exothermic reaction and pass 0 directly into themetal bath, under protection of the slag covering, and thussubstantially prevent the reduced alloying metal or metals becomingoxidized and passing off into the slag. In carrying forward theinvention upon these lines it has been found that important features arethat the process involving the use of the invention supplies a simple,cheap and eflicient means for alloying a bath of ferruginous moltenmetal with the alloying metal, such as chromium, since the ore of thealloying metal may be applied direct to the molten body or bath of themetal to. be alloyed; and, according to the present invention it ispossible to use a lower grade of alloying ore (such as a low grade orecontaining chromium) than was heretofore possible. It has actually beendetermined in practice that according 'to the present invention thealloying process can successfully be carried out with theuse of a lowgrade chrome ore having a ratio of chromium to iron of. 1.7 to 1, thatis, an ore having approximately 40% chromium sesquioxide, whereasaccording to prior practicesfit, has only been possible to successfullycarry out the alloying operation with the use of amore costly high gradechrome ore having a ratio of 3 to 3 of chromium to 1 of iron, that is anore averaging about 50% CrzOa.

Also, an important consideration in carrying forward the invention isthat it can be applied, without alterations, to existing plants whichoperate either the basic open hearth or basic electric furnaces and thatat the termination of the alloying period, according to the presentinvention, the molten bath of metal is thoroughly deoxidized. andmaintains suflicient heat and fluidity for tapping and teeming.

Furthermore, in carrying out the method of alloying, according to thepresent invention, the resulting ingots are sound and satisfactorilyforge out, and upon rolling into strip a pronounced feature ofimportance has been found in the fact that the edges of the strip arefree from rupture and ragged selvage, such as ordinarily occurs and mustbe removed as scrap, with consequent loss. Ordinarily high chromiumcontent steels are not made in the open-hearth furnace owing to thestrong oxidizing atmosphere of this furnace, but under my procedureherein explained. it is possible to produce such steel in the openhearthfurnace and the direct loss by oxidation of the alloyed chromium wouldbe considerably 1655, since my process uses a cheaper low grade chromiumas against the more costly specially made low-carbon ferro-chrome.

It has also been found that finished material made according to thepresent invention presents a finer and denser grain and smoother surfacethan is known to the applicant in any finished alloyed material madeaccording to any present or standard practice.

As distinguished from prior practices which are operated at relativelyhigh cost, and with .highly specialized technique, and in some casesunder prohibitive and dangerous conditions, the present inventiongenerally has in view an economical and eflicient method of making ironor steel alloy having a high percentage of alloying metal with a, lowcarbon content, which method can be carried out satisfactorily in eitheran open hearth or an electric furnace; also the present inventioninvolves the use of inexpensive alloying and reducing materials, thereactions between which are exothermic and utilized to keep the metalhot and fluid.

And finally, it is an object of the present invention to provide animproved method'of making low carbon, high chromium or other alloysteels' fi'n which the alloying and reducing materials are maintained incontact with the surface of the metal bath below the slag duringreduction, so as to accelerate the reduction and prevent .thealloying,.metal frombecoming oxidized and passing into the slag.

These and other objects are attained by the improvements comprising thepresent invention, which may be stated in general terms as comprising amethod of making an alloy iron or steel and/or other alloyable metals,including the step of adding to the metal bath relatively heavy moldedblocks containing one or more oxides of the alloying metal and a metalsilicide, said blocksbeing adapted to penetrate the slag and come indirect contact with the surfaceof the molten metal of the bath.

By the method which I now describe, and which I have commercially workedout with success, I am able to advantageously make use 0f the basicopen-hearth furnace for low carbon high chromium steels, without anyundue loss SeSqui oxide of chromium-i-silicon=chromium+ silica Ferrousoxide+silicon=iron+silica A slight excess of the chromite may be used toprevent any silicon from remaining unoxidized and alloying with thereduced metal. To these ingredients, slaked lime (calcium hydrateCaHzOz) is added, preferably in powdered form in sufficient quantity tocombine with and partly flux the silica formed by the above reactionsand to bind these ingredients together, or this bond may be provided forby using a chloride solution of an alkaline earth, such as chloride ofmagnesium;

They are then thoroughly mixed together, after which just suflicientwater is added to make a plastic mass suitable for molding, beingpreferably well pugged in any suitable mill. The pugged mass is thenpreferably molded into relatively heavy blocks or pieces of convenientform, size and shape for the. furnace men to handle, and'may consist ofblocks 8"x'10"x6" weighing forty to fifty pounds. When the molded piecesor blocks are introduced on to the surface of the metal bath, being ofgreater density and/or weight than the slag on the bath, they willdisplace the slag and come into direct contact with the surface of themolten metal beneath the slag layer.

otherwise to a milk of lime wash. After that" when sufliciently dried,they are preferably transferred to any suitable drying oven or kiln,where the excess or free water is expelled. They can.,then beeitherheated upin this ,chamber, or transferred to a separate heating chamberwhich is brought up to a temperature preferably in excess of 1650 F., orin the range of temperatures between 700 C. to 1000" C., as. heretoforeexplained. Practical operations have shown that this heating isnecessary to drive off combined or colloidal water formed by thechemical reaction upon air drying of the pugged mass of ore and lime,thus not only to completely dehydrate the pieces or blocks, but also, ofessential importance, to also completely degasify the same and therebyprevent the bath of such bath being ruined thereby. The heated moldedpieces may now be withdrawn from the heating chamber as required, andwhile hot are of molten metal absorbing gases with the danger ready tobe charged directly into the melting furnace holding the bath ofmetal-for alloying therewith. I

The usual procedure may be followed in preparing the bath of moltenmetal in an openhearth furnace, and the oxidizing slag formed during themelting stage is removed, after which a fresh slag of fluorspar, lime,and ferro-silicon may be added. The additions of the alloying metal arethen made by introducing the molded pieces or blocks onto the metalbath, as stated- The usual necessity of superheating the bath of metalbefore each addition is avoided, because the chemical reactions takingplace on the surface of the metal bath producedand between the chromiteand ferro-silicon are exothermic, and the heat thus given off istransferred to the metal bath and keeps the same hot and fluid. At theend of the alloying period, the bath of metal is sufliciently hot andkilled to tap and teem into molds, where the metal rests perfectlytranquil or quiescent. The term killed as applied to steel means steelwhich is sumciently deoxidized to be quiescent in the molds.

An important advantage of the molded pieces or blocks is that theyharden upon being kept and do not spall or disintegrate when thrown onto the metal bath at the temperature of the steel melting furnace. Also,no matter how the alloy? ing pieces or blocks are, thrown into themolten bath they will always right themselves so that the largest orheaviest side will fioat downwardly in direct contact with the surfaceof the metal bath. Due to the density and weight of the compact materialof the relatively heavy molded pieces being greater than that of themoltenslag, they will quickly penetrate or displace the slag and comeindirect contact with the surface of the metal bath.

With the molded pieces in direct contact with the surface of the metalbath, and the intimate contact between the chromite and the ferrosiliconmolded together in the molded pieces, the reduction proceeds rapidlybelow the slag in contact with the surface of the bath of metal and asthe alloying metals are released by the reactions ferro-chrome, and lowcarbon ferro-silicon can be made economically, the alloying and reducingmaterials employed are relatively inexpensive.

Moreover, alloy steels having a. high percentage of the alloying metalswith a low carbon content can be produced by the improved method with agreat saving in time, cost of material and operating, and in recovery oryield.

While I have described my improved method as applied to the productionof high chromium low carbon alloy steels, the method islikewiseapplicable to the making of similar iron and steel alloys of numerousother alloying metals, such as tungsten and vanadium.

Also, the improved method is applicable to the production of alloysteels having a higher percentage of carbon and a lower percentage ofthe alloying metals.

It will be seen from the foregoing that one of the distinctive featuresof the present invention resides in the fact that in the so-called pieceor block of alloying material the alloying and reducing materials areheld in such compact con- 5 dition that each particle of these materialsis in intimate relation. Thus, full use is made of the exothermicreactions during the period of reduction, that is, the heat evolved fromsuch reactions is carried into and disseminated throughout the bath ofmolten metal. This insures the alloyed metal being cast in a deoxidizedand homogenous condition, thus minimizing to a very great degree thelosses which usually are due to surface and edge defects. At the sametime the process utilizing the pieces or blocks of alloyingmaterial madein accordance with the present invention results in an alloy having animproved molecular structure that is one in which a very fine closegrain prevails with a smooth surface in the finished strip free fromimperfections such as irregularities and projecting pimples or bumps.These results are quite definitely obtained because of the exothermicaction taking place within and between the piece or block of alloyingmaterial and the molten metal of the molten bath. Substantial heat isevolved by this action and the alloying metal is released from the pieceor block into the molten metal bath, becoming diffused or in solutiontherewith, and at the same time carrying the greater part of the heat ofthe said exothermic action with it, thereby materially contributing tomaintaining the heat of the finished alloy so that it can be drawn offand teemed.

It will also be understood that in carrying out the invention that thesame contemplates the use of alloying metals other than chromium, andalso includes and takes into consideration the fact that more than onealloying metal may be embodied in the finished piece or block ofalloying 40 material so that the term alloy-containing ore as usedherein is employed in a generic sense.

While I have described my improved method as carried out in theopen-hearth furnace, it maybe carried out satisfactorily in the electricfurnace or any other suitable type or kind of furnace supplying heatthroughout the process, without departing from the scope of theinvention as defined in the appended claims.

I claim: g

1. In a method of making alloys of iron and steel, including preparing asuitable bath 'of ferruginous molten metal, in any suitable type or kindof furnace supplying heat throughout the process, removing the oxidizingslag accumulated during the -melting stage, and covering the metal bathwith a fresh slag, composed of lime and fluorspar, to which a smallquantity of ferrosilicon is added, the step of introducing on to thesurface "of the metal bath relatively heavy molded blocks containing oneor more of the oxides of the alloying materials and a noncarbonaceousreducing agent, all in a comparatively fine state of division, beingcemented together with the aid of slaked lime and'water, and being ofsuch density as to penetrate the slag and come into direct contact withthe surface of the molten metal of the bath, such molded blocks, afterbeing air dried, are sprayed over with a milk of lime wash and allowedto dry, are then heated up to a temperature in excess of 1650 F. for thepurpose of pugged mass of ore and lime.

2. In a method of making alloys of iron and 76 steel. includingpreparing a suitable bath of ferruginous molten metal, in any suitabletype or kind of furnace supplying heat throughout the process, removingthe oxidizing slag accumulated during the melting stage, and coveringthe metal bath with a fresh slag composed of lime and fluorspar, towhich a small quantity of ferrosilicon is added, the step of introducingon to the surface of the molten bath relatively heavy molded blockscontaining one or more of the oxides of the alloying materials and anoncarbonaceous reducing agent, all in a comparatively fine state ofdivision, being cemented together by the aid of slaked lime and water,such molded blocks having been air dried, are sprayed over with a milkof lime wash and allowed to dry, and are then heated up to a temperaturein excess of 1650 F. to free them of any combined water formed by thechemical reaction upon air drying of the pugged mass of ore and lime, sothat, when coming into contact with the surface of the molten bath ofmetal, there will be no absorption of gases by the molten bath of metalfrom the molded blocks, and the heat developed due to the exothermicchemical reaction between the materials of the molded blocks is thustransferred direct to the molten bath of metal by the jecting the saidbody precipitation of the reduced alloying metal or metals.

3. The method of preparing metal alloying material consisting of forminga compacted body of intermixed particles of alloy-containing ore andreducing agent, bonding or cementing said particles together by anhydrated oxide of an alkaline earth, pre-drying said compact body ormass, surface treating said pre-dried body or mass with a milk of limewash, drying same, and finally heating the treated body or mass to atemperature causing dehydration and degassing thereof.

4. The method of making ferruginous alloys which consists in firstpreparing a mass of molten metal, separately forming a compacted body ofintermixed particles of alloy-containing oreand of a reducing agentbonded together by the hydroxide of an alkaline earth, subsequentlysubto a temperature not less than 700 cent., causing the liberationtherefrom of free, combined and colloidal water and then bringing thesaid body, while in a heated condition, into direct contact with themolten metal.

5. The method of making ferruginous alloys which consists in firstpreparing a mass of molten metal, separately preparing a compacted bodyformed of intermixed particles of alloy-containing ore and of asilicon-containing reducing agent bonded together by the hydroxide of analkaline earth, subsequently subjecting the said body to a temperaturenot less than 700 cent., causing the liberation therefrom offree-combined and colloidal water and then bringing the said body, whilein a heated condition, into contact with the molten metal. 7

6. The method of making ferruginous alloys which consists in firstpreparing a mass of molten metal, separately preparing a compacted bodyof intermixed particles of chrome ore and of a said body to atemperature sufliciently high to cause dehydration and degassing thereofand to convert thesaid hydroxide into the oxide of said alkaline earthpreliminary to bringing the body, while in a heated condition, intosurface contact with the molten metal.

8. The method of making ferruginous alloys which consists in firstpreparing a mass of molten metal, separately preparing a compacted bodyof intermixed ground particles of chrome ore and ferro-silicon bondedtogether bythe hydroxide of calcium and subsequently subjecting saidbody to a temperature sufficiently high to cause dehydration anddegassing thereof and to convert the said hydroxide into the oxide ofsaid calcium preliminary to bringing the body, while in a heatedcondition, into surface contact with the molten metal.

9. The method of making ferruginous alloys which consists in firstpreparing a mass of molten metal, separately preparing a. mix, withwater, of

particles of alloy-containing ore and of ferro- I silicon, bonding saidparticles together by the hydroxide of an alkaline earth, andsubsequently subjecting the said mix to a temperature in excess of 700cent. preliminary to bringing the mix into contact with the moltenmetal,

10. The method of preparing metal alloying material consisting offorming a compacted body of intermixed ground particles ofalloy-containing ore and of a silicon-containing reducing agent, bondingsaid particles together by the hydroxide of an alkaline earth,pre-drying said compacted body, and subsequently heating said body to atemperature in excess of 700 cent; caus-v ing the dehydration anddegassing thereof.

CASIMIR JAMES HEAD.

